GPR systems may be used for the identification of buried objects. GPR systems are generally described in U.S. Pat. No. 6,496,137 of Johansson which is entitled “Ground Penetrating Radar Array and Timing Circuit.” Unlike upward-looking radar used for air traffic control and meteorology, an antenna array in a GPR is directed toward the ground and can be used for geophysical applications such as mapping subsurface strata, locating toxic waste sites for remediation, and detecting of unexploded subsurface ordinance. The Johansson U.S. Pat. No. 6,496,137 is incorporated herein by reference.
The systems and methods described in the Johansson patent include a first delay circuit for receiving a transmit timing input signal and for generating a number of intermediate transmit timing signals delayed with respect to each other by a delay time. A transmit output switch circuit selects either the transmit timing input signal or a corresponding one of the intermediate transmit timing signals as a corresponding output transmit timing signal. Similarly, the Johansson patent discloses a second delay circuit for receiving the receive timing input signal and for generating a number of intermediate receive timing signals delayed with respect to each other by a delay time. A shift-delay circuit is coupled to the second delay circuit and the receive timing input signal to add the delay time to the intermediate receive timing signals. A receive output switch circuit selects either the receive timing input signal or a corresponding one of the intermediate receive timing signals as a corresponding output receive timing signal.
There is, however, a need for faster, highly accurate timing systems capable of timing multiple transmit and receive antennas to accurately image the subsurface. A timing system of this type that can be efficiently implemented would be especially desirable.